This invention relates to a damping valve unit for a hydraulic oscillation damper of the type described as follows:
A damping valve unit comprises a basic constructional assembly. The basic constructional assembly has an axis, a radially outer cylindrical face and an axially directed annular valve face. The axially directed annular valve face surrounds the radially outer cylindrical face and is radially spaced from said radially outer cylindrical face.
The damping valve unit further comprises a first substantially planar valve disc axially movable along said radially outer cylindrical face and having a radially inner circumferential edge adjacent said radially outer cylindrical face, a radially outer circumferential edge, a first side face engageable with said axially directed annular valve face, and a second side face axially remote from said first side face.
The damping valve unit further comprises a second substantially planar valve disc, said second substantially planar valve disc being axially movable along said radially outer cylindrical face and having a radially inner circumferential edge adjacent said radially outer cylindrical face, a radially outer circumferential edge, a first side face adjacent said second side face of said first valve disc and a second side face axially remote from said first valve disc.
The damping valve unit further comprises an annular valve member axially slidable along said radially outer cylindrical face, said valve member having axially directed contact face means engageable with said second side face of said second valve disc and being axially biased towards said second side face of said second valve disc, such as to urge said second valve disc towards said first valve disc and said first valve disc towards said axially directed annular valve face.
A liquid distribution space means is provided adjacent said first side face of said first valve disc and radially inwards of said axially directed annular valve face. This liquid distribution space means is in liquid flow connection with a first working chamber of the hydraulic oscillation damper.
A liquid collection space means is provided adjacent the radially outer edges of said first and second valve disc. This liquid collection space means is in liquid flow connection with a second working chamber of the hydraulic oscillation damper.
The first valve disc is liftable from the axially directed annular valve face in response to a predetermined pressure difference between a higher liquid pressure within said first working chamber and a lower liquid pressure within said second working chamber, such as to open a liquid flow passage between said first working chamber and said second working chamber.
A preliminary restricted liquid flow passage exists between said liquid distribution space means and said liquid collection space means below said predetermined pressure difference. This preliminary liquid flow passage extends in series across the radially inner circumferential edge of said first valve disc, through radially inner edge recesses of said radially inner circumferential edge of said second valve disc and through radially outer edge recesses of said radially outer circumferential edge of said second valve disc.
This type of damping valve unit is e.g. used as a traction valve in a hydraulic oscillation damper. The traction valve is provided on a damping piston of the hydraulic oscillation damper and has the function to damp axially outward movement of the piston rod with respect to the cylinder of the hydraulic oscillation damper.
Hydraulic oscillation dampers, particularly for motor vehicles, are produced in large series. It is necessary that the oscillation dampers and the components thereof comprise simple parts easy to be manufactured. It is further necessary that the assembling of the hydraulic oscillation dampers and of its components is easy. Further it is necessary that the damping function is substantially identic for the hydraulic oscillation dampers of a series of production. A further request is that in operation of the hydraulic oscillation damper, noise resulting from liquid flow through the valves and particularly through the traction valve is substantially eliminated.